Question

What is true about unmyelinated nerve fibre?

• A. Not enclosed by both Schwann cells and a myelin sheath
• B. Enclosed by Schwann cells that do not form a myelin sheath
• C. Not enclosed by Schwann cells but enclosed by a myelin sheath
• D. Not found in the autonomous and the somatic neural system

Answer 1

The correct option is B

Enclosed by Schwann cells that do not form a myelin sheath

The correct option is B.

Explanation of the correct option:

1. Unmyelinated, or type C, fibres have axons that are both peptidergic (for heat/cold sensitivity) and nonpeptidergic (for mechanical sensitivity).
2. They are completely devoid of the myelin sheath.
3. Schwann cells, which do not create a myelin sheath around the axon, encase unmyelinated nerve fibres.
4. The autonomous and somatic neuronal systems contain them.

Explanation of the incorrect option:

Option A:

1. Schwann cells are essential in the PNS in response to axon damage because they can aid in axon regeneration in addition to insulating axons.
2. Axonal degeneration and cell death are both possible outcomes of any axonal damage.

Option C:

By concentrically wrapping its plasma membrane around the inner axon, a Schwann cell creates a myelin sheath.

Option D:

These are found in autonomous and somatic nervous systems.

Final answer: Unmyelinated nerve cells are enclosed by Schwann cells that do not form a myelin sheath.